Add .clang-format file compatible with Clang12.

Config file template generated with
`clang-format-12 --style=llvm --dump-config > .clang-format`
And adjusted to fit K&R style.

Signed-off-by: Mateusz Starzyk <mateusz.starzyk@mobica.com>

.clang-format

@@ -0,0 +1,113 @@
+---
+Language: Cpp
+AlignAfterOpenBracket: Align
+AlignConsecutiveAssignments: false
+AlignConsecutiveBitFields: Consecutive
+AlignConsecutiveDeclarations: false
+AlignConsecutiveMacros: Consecutive
+AlignEscapedNewlines: Left
+AlignOperands: true
+AlignTrailingComments: false
+AllowAllArgumentsOnNextLine: false
+AllowAllParametersOfDeclarationOnNextLine: false
+AllowShortBlocksOnASingleLine: false
+AllowShortCaseLabelsOnASingleLine: false
+AllowShortEnumsOnASingleLine: false
+AllowShortFunctionsOnASingleLine: None
+AllowShortIfStatementsOnASingleLine: false
+AllowShortLoopsOnASingleLine: false
+AlwaysBreakAfterDefinitionReturnType: None
+AlwaysBreakAfterReturnType: None
+AlwaysBreakBeforeMultilineStrings: false
+AlwaysBreakTemplateDeclarations: false
+BinPackArguments: true
+BinPackParameters: false
+BitFieldColonSpacing: Both
+BreakBeforeBinaryOperators: None
+BraceWrapping:
+  AfterCaseLabel:  false
+  AfterControlStatement: Never
+  AfterEnum:       false
+  AfterFunction:   true
+  AfterStruct:     false
+  AfterUnion:      false
+  AfterExternBlock: false
+  BeforeElse:      false
+  BeforeWhile:     false
+  IndentBraces:    false
+  SplitEmptyFunction: true
+  SplitEmptyRecord: true
+  SplitEmptyNamespace: true
+BreakBeforeBraces: Custom
+BreakBeforeInheritanceComma: false
+BreakBeforeTernaryOperators: false
+BreakStringLiterals: false
+ColumnLimit: 80
+# CommentPragmas prevent formatting of comments fitting particular patterns.
+# Clang-format accepts only one pragma, so we need too prepapre a list of patterns joined with "|".
+# * test cases: BEGIN_CASE|END_CASE
+# * special string for check-names script: ^no-check-names
+# * doxygen blocks: \\name|\\brief|\\param|\\return|^ {11}|\{.*\}
+#    The '^ {11}' stands for minimal indent in multiline Doxygen comments.
+#    It comes from the length of \brief keyword + 1 space prefix before the keyword
+#    and 4 spaces suffix after it, as in: " * \brief    Function description ..."
+#                                            ^_________^
+# * KreMLin code generation: "KreMLin invocation"
+CommentPragmas: 'BEGIN_CASE|END_CASE|^no-check-names|\\name|\\brief|\\param|\\return|^ {11}|\{.*\}|KreMLin invocation'
+ContinuationIndentWidth: 4
+Cpp11BracedListStyle: false
+DerivePointerAlignment: false
+DisableFormat: false
+ExperimentalAutoDetectBinPacking: false
+ForEachMacros: []
+IncludeBlocks: Preserve
+IncludeCategories:
+ - Regex: '.*'
+   Priority: 1
+IncludeIsMainRegex: '(Test)?$'
+IndentCaseBlocks: true
+IndentCaseLabels: true
+IndentExternBlock: NoIndent
+IndentGotoLabels: false
+IndentPPDirectives: AfterHash
+IndentWidth: 4
+IndentWrappedFunctionNames: false
+KeepEmptyLinesAtTheStartOfBlocks: false
+MacroBlockBegin: ''
+MacroBlockEnd: ''
+MaxEmptyLinesToKeep: 1
+PenaltyBreakAssignment: 10
+PenaltyBreakBeforeFirstCallParameter: 30
+PenaltyBreakComment: 10
+PenaltyBreakFirstLessLess: 0
+PenaltyBreakString: 50
+PenaltyExcessCharacter: 100
+PenaltyReturnTypeOnItsOwnLine: 60
+PointerAlignment: Right
+ReflowComments: true
+SortIncludes: false
+SortUsingDeclarations: true
+SpaceAfterCStyleCast: false
+SpaceAfterLogicalNot: false
+SpaceAroundPointerQualifiers: Default
+SpaceBeforeAssignmentOperators: true
+SpaceBeforeCaseColon: false
+SpaceBeforeParens: ControlStatements
+SpaceBeforeSquareBrackets: false
+SpaceInEmptyBlock: false
+SpaceInEmptyParentheses: false
+SpacesBeforeTrailingComments: 1
+SpacesInAngles: false
+SpacesInContainerLiterals: false
+SpacesInCStyleCastParentheses: false
+SpacesInConditionalStatement: false
+SpacesInParentheses: false
+SpacesInSquareBrackets: false
+Standard: Cpp11
+StatementAttributeLikeMacros: []
+StatementMacros: []
+TypenameMacros: ['MBEDTLS_PRIVATE']
+UseCRLF: false
+UseTab: Never
+WhitespaceSensitiveMacros: []
+...